System and method for autonomously scanning and processing a part

ABSTRACT

One variation of a method for autonomously scanning and processing a part includes: accessing a part model representing a part positioned in a work zone adjacent a robotic system; retrieving a sanding head translation speed; retrieving a toolpath for execution on the part defining positions, orientations, and target forces applied by the sanding head to the part. The method includes traversing the sanding head along the toolpath, at the sanding head translation speed; reading a sequence of applied forces from a force sensor coupled to the sanding head at positions along the toolpath; and deviating from the toolpath to maintain the set of applied forces within a threshold difference of a sequence of target forces along the toolpath. In one variation of the method, the robotic system executes a toolpath at a duration less than target duration by selectively varying target force and sanding head translation speed across the part.

CROSS-REFERENCE TO RELATED APPLICATIONS

This Application is a continuation of U.S. application Ser. No.17/826,867, filed on 27 May 2022, which is a continuation-in-part ofU.S. application Ser. No. 17/390,885, filed on 31 Jul. 2021, whichclaims the benefit of U.S. Provisional Application No. 63/059,932, filedon 31 Jul. 2020, each of which is incorporated in its entirety by thisreference.

TECHNICAL FIELD

This invention relates generally to the field of automated finishing andmore specifically to a new and useful method for autonomously processinga part in the field of automated finishing.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a schematic representation of a first method;

FIG. 2 is a schematic representation of a variation of the first method;

FIG. 3 is a schematic representation of a variation of the first method;

FIG. 4 is a flowchart representation of a variation of the first method;

FIG. 5 is a flowchart representation of a variation of the first method;and

FIG. 6 is a flowchart representation of a variation of the first method.

DESCRIPTION OF THE EMBODIMENTS

The following description of embodiments of the invention is notintended to limit the invention to these embodiments but rather toenable a person skilled in the art to make and use this invention.Variations, configurations, implementations, example implementations,and examples described herein are optional and are not exclusive to thevariations, configurations, implementations, example implementations,and examples they describe. The invention described herein can includeany and all permutations of these variations, configurations,implementations, example implementations, and examples.

1. System

As shown in FIGS. 1-6 , a system 100 for autonomously scanning andprocessing a part includes a robotic manipulator 110 arranged adjacent awork zone, including an end effector 112 defining a sanding head 120 andan optical sensor 114. The robotic manipulator 110 is configured to,during a scan period: autonomously translate an optical sensor 114across a part arranged within the work zone; and capture a set ofoptical images. The robotic manipulator no is further configured to,during a processing period: move the sanding head 120 along a toolpath;monitor a force value of the sanding head 120 on the part; and deviatefrom the toolpath to align the force value to a target sanding force onthe part.

The system 100 further includes a controller 115 configured to, duringthe scan period: receive the set of optical images; assemble the set ofoptical images into a part model representing the part; access a set oftool characteristics of the sanding head 120 mounted to the roboticmanipulator 110; generate the tool path defining a sequence of positionsalong the part model; and define the target sanding force based on theset of tool characteristics.

2. Method

As shown in FIGS. 1-6 , a method S100 for autonomously scanning andprocessing a part includes, during a scan cycle: autonomouslymanipulating a robotic system to move an optical sensor 114 across apart loaded into a work zone; and, at the optical sensor 114, capturinga set of optical images depicting the part. The method S100 alsoincludes: assembling the set of optical images (e.g., 2D images, 3Dimages) into a part model representing the part in Block Silo; accessinga set of tool characteristics of a sanding head 120 mounted to therobotic system; characterizing surface contours within the part model;detecting a first region within the part model exhibiting a firstsurface contour accessible to the sanding head 120 based on the set oftool characteristics; and detecting a second region within the partmodel exhibiting a second surface contour inaccessible to the sandinghead 120 based on the set of tool characteristics in Blocks S120, S112.The method S100 further includes: defining a set of keypoints on thefirst region within the part model; and, for each keypoint in the set ofkeypoints, defining a position of the sanding head 120 on the part,defining an orientation of the sanding head 120 on the part, defining atarget force value of the sanding head 120 on the part, and assemblingthe set of keypoints into a toolpath for execution by the robotic systemin Block S140.

One variation of the method S100 includes accessing a part modelrepresenting a part and accessing a geometry 123 of sanding pad 121 inBlock S120.

This variation of the method S100 also includes: characterizing surfacecontours within the part model by detecting local contour radii ofsurface contours in Block S112; detecting a first region within the partmodel exhibiting a first surface contour accessible to the sanding head120 based on the geometry 123 of sanding pad 121 in Block S120; anddetecting a second region within the part model exhibiting a secondsurface contour inaccessible to the sanding head 120 based on thegeometry 123 of sanding pad 121 Block S120.

This variation of the method S100 further includes in Block S140,generating a toolpath in by: defining a series of position andorientation pairs located in the first region of the part model;calculating a contact area of the sanding head 120 on the part at theseries of position and orientation pairs based on a ratio of thegeometry 123 of sanding pad 121 to the local contour radii at the seriesof position and orientation pairs in Block S130; and annotating theseries of position and orientation pairs with a target force based onthe contact area in Block S142.

Another variation of the method S100 includes: accessing a part modelrepresenting surface contours of a part loaded into a work zone proximala robotic system and accessing a set of tool characteristics of asanding head 120 manipulated by the robotic system, the set of toolcharacteristics including a geometry 123 of the sanding pad 121 and acompliance 126 of a backing 125 supporting the sanding pad 121;retrieving a toolpath pattern; and retrieving a set of nominalprocessing parameters in Block S140. This variation of the method S100also includes: projecting the toolpath pattern onto the part model todefine a toolpath in; and defining a set of regions along the toolpathin Block S140. This variation of the method S100 further includes, foreach region in the set of regions of the toolpath: detecting a localcurvature radius of surface contours represented in the part modelproximal the region of the toolpath in Block S112; calculating a contactarea between the sanding head 120 and the part proximal the region basedon the geometry 123 of the sanding pad 121, the compliance 126 of thebacking 125, and the local curvature radius in Block S130; and defininga target execution value, in a set of target execution values, of thesanding head 120 on the part based on the contact area and the set ofnominal processing parameters in Block S142. This variation of themethod S100 also includes, during a processing cycle, at the roboticsystem: navigating the sanding head 120 along the toolpath in BlockS150; reading a sequence of execution values from a sensor in therobotic system in Block S152; and deviating from the toolpath tomaintain the sequence of execution values within a threshold differenceof the set of target execution values in Block S154.

Another variation of the method S100 includes: accessing a part modelrepresenting surface contours of a part loaded into a work zone adjacenta robotic system in; accessing a geometry 123 of a sanding head 120manipulated by the robotic system; retrieving a toolpath pattern;projecting the toolpath pattern onto the part model to define atoolpath; and defining a set of regions along the toolpath in BlockS140. This variation of the method S100 also includes, for each regionin the set of regions of the toolpath: detecting a local curvatureradius of surface contours represented in the part model proximal theregion of the toolpath Block S112; calculating a contact area betweenthe sanding head 120 and the part surface proximal the region and thelocal curvature radius Block S130; and defining a target force value, ina sequence of target force values, of the sanding head 120 on the regionof the part based on the contact area Block S142. This variation of themethod S100 further includes, during a processing cycle, at the roboticsystem: navigating the sanding head 120 along the toolpath Block S150;reading a sequence of force values from a force sensor 116 coupled tothe sanding head 120 Block S152; and deviating from the toolpath tomaintain the sequence of force values within a threshold difference ofthe sequence of target force values Block S154.

3. Applications

Generally, Blocks of the method S100 can be executed or controlled by acontroller 115 (or other computer system) in conjunction with a roboticsystem to complete a work cycle, including autonomously scanning a partloaded into a work zone proximal the robotic system, and executing aprocessing protocol on the part.

The controller 115 can execute a rapid, first scan (e.g., under oneminute to complete image capture, under one minute to process imagesinto a part model) of a part loaded in the work zone to determine thedimensions and properties of the part, such as contour and color, aswell as detect edges indicating features or boundaries of the part. Therobotic system executes the first scan by sweeping an optical sensor 114(e.g., an RGB color camera, a LIDAR sensor, a stereoscopic camera) overthe area of the work zone to: capture a set of optical images depictingthe part; detect the part within the set of images; and assemble the setof images into a three-dimensional model of the part. The controller 115can define a toolpath executable by the robotic system in machinecoordinates and project the toolpath onto the three-dimensional model.

The robotic system can then move a sanding head 120 to execute thetoolpath on the part with a low accuracy (i.e., tolerance greater than 1in.) and deviate the sanding head 120 from the toolpath to achieve atarget force between the sanding head 120 and the part surface. Inparticular, the robotic system can orient the sanding head 120 such thatan axis of rotation of the sanding head 120 is coaxial with a vectornormal to the part and translate the sanding head 120 along the axistoward or away from the part to achieve the target force.

The robotic system tightly controls the force of the sanding head 120 onthe part, therefore the robotic system can compensate for errors in thefirst scan by tightly controlling the force exerted on the part by thesanding head 120. By utilizing a first scan, the overall execution timenecessary to scan and process the part (i.e., complete a work cycle) isreduced, resulting in a higher throughput for the system as opposed to alonger duration scan.

Generally, the controller 115 defines a target force to exert on thepart. The target force can be constant across the part, or modulatedbased on the properties of the part or the parameters of the processprotocol. Target force is generally defined based on: the grit 122 of asanding pad 121 attached to the sanding head 120; the geometry 123 ofsanding pad 121; the material composition of the part or coating on thepart; the traversal speed of the sanding head 120 across the part; thelocal contour radius of the part surface along the toolpath, whichdetermines the contact area of the sanding head 120 on the part surface;the shape of the contour (i.e., concave or convex); and the compliance126 of a backing 125 pad supporting the sanding pad 121.

The controller 115 can access a part processing profile to define thetarget force on a specific part. A part processing profile containsprocessing protocol parameters and part attributes. Processing protocolparameters define sets of characteristics (such as grit 122 of sandingpad 121) and actions (such as translation speed) of the robotic systemduring a particular process such as stripping paint, preparing primer,or buffing a final paint coat. Part attributes describe inherentcharacteristics of a part type, such as material type, part geometry123, and maximum pressure. The robotic system retrieves the parametersof a particular process protocol for a particular part type to executethe particular process protocol on an individual part.

The robotic system can execute the same process for a variety of parttypes (e.g., a paint stripping process on a car door and a furniturepiece), or a variety of processes on the same part type (e.g.,stripping, primer preparation, and final paint buffing on a single carhood) by selecting the correct profile or profile attributes.

A collection of part processing profiles can be pre-loaded onto therobotic system, or part processing profiles can be entered manually byan operator. Additionally or alternatively, the robotic system canaccess an operator profile defining operator preferences for aprocessing cycle, such as a sanding head 120 translation speed, ageneric toolpath pattern, or default applied force value.

Therefore, the controller 115 can develop a low-tolerance toolpath(e.g., +/−one inch) on a part surface in near real-time based on a firstscan of the part. The robotic system can then achieve high-resolutionsurface processing by achieving a target applied force of the sandinghead 120 through detecting the applied force in real-time at the sandinghead 120 and selectively deviating from the low-resolution toolpath tomaintain the target applied force along the length of the toolpath.Thus, the robotic system achieves high resolution accuracy and highrepeatability of a process protocol by combining a low-resolution scanwith high accuracy target force execution derived from other processingparameters.

4. System

In one implementation as shown in FIGS. 1, 3, and 4 , the systemincludes: a robotic system arranged adjacent to a work zone defining: arobotic manipulator 110 configured to translate an end effector 112,mounted to the robotic manipulator no, through six degrees of freedom upto the spatial limits of the work zone during a work cycle.

An optical sensor 114 is mounted to the end effector 112 and configuredto capture color and depth maps (i.e., a RGB color camera, a LIDARsensor, a stereoscopic camera).

A random orbital sanding head 120 (hereinafter referred to as a “sandinghead 120”) is mounted to the end effector 112 and configured to rotate asanding pad 121 (e.g., a sanding disk, a sanding sheet, a sanding wheel)affixed to a compliant backing 125. A force sensor 116 is located at thesanding head 120 and configured to detect a force on the sanding head120 normal to the surface of the sanding pad 121 at the center of thesanding pad 121. In one variation of the implementation, the sandinghead 120 is another type of abrasive device such as an orbital sander, avibrating or “mouse” sander, a rotary tool, a wire brush wheel, etc.

In one implementation, the robotic system includes a linear actuator 118mounted to the end effector 112 coaxial with an axis of rotation of thesanding head 120, and configured to extend and retract the sanding head120 from the end effector 112. In one variation, the linear actuator 118is an electromechanical actuator configured to detect resistance toextension or retraction of the sanding head 120 in real time. In anothervariation, the linear actuator 118 is a pneumatic cylinder including apressure sensor configured to detect the air pressure in the cylinder inreal-time.

In one example, the robotic manipulator 110 includes a force sensor 116coupled to the sanding head 120 and configured to output signalsrepresenting the force value of the sanding head 120 normal to localareas of the part in contact with the sanding head 120. The controller115 then defines the target sanding force normal to local areasrepresented in the part model and inversely proportional to radii oflocal areas represented in the part model.

In another example: the sanding head 120 includes a compliant backing125: configured to locate and support a sanding pad 121; configured toelastically deform in response to application of the sanding pad 121onto the part; and characterized by a compliance 126 coefficient. Therobotic manipulator 110 further includes a force sensor 116 coupled tothe sanding head 120 and configured to output signals representing theforce value of the sanding head 120 normal to local areas of the part incontact with the sanding head 120, and the controller 115 defines thetarget sanding force normal to local areas of the part model andproportional to the compliance 126 coefficient.

The robotic system further includes a controller 115 configured to:control the components of the robotic system; store operator profilesand part processing profiles; assemble a set of color images (e.g.,color images, stereoscopic images, depth maps) into a part model andannotate the part model with additional data; define keypoints andassemble toolpaths in machine coordinates; calculate force values basedon attributes of the sanding head 120, detected attributes of the part,an operator profile, and/or a part processing profile; and present datato, and receive data from, a user via a user interface.

In one implementation, the robotic system includes additional sensorsincluding: a force sensor 116 at an actuating joint of the roboticmanipulator 110; a torque sensor arranged at the sanding head 120configured to detect a torque value at the axis of rotation of thesanding head 120; a position sensor arranged at the sanding head 120configured to detect rotation of the sanding head 120.

In one implementation, the robotic system includes multiple opticalsensor 114 s arranged about the perimeter of the work zone, the fieldsof view of the optical sensor 114 s oriented toward the interior of thework zone, and configured to capture optical color and depth maps.

In another implementation, the robotic manipulator 110 defines asix-axis gantry arranged over work zone.

In another implementation, the robotic manipulator no defines amulti-link robotic arm mounted on a linear conveyor 130 configured totranslate the length of the work zone.

In one example, the robotic manipulator no defines a multi-link roboticarm configured to manipulate the end effector 112 through six degrees offreedom proximal the part positioned in the work zone; and a linearconveyor 130 configured to translate the multi-link robotic arm thelength of the work zone.

4.1 Tool Profile

In one implementation, the controller 115 stores a tool profile definingthe end effector 112 dimensions, including the dimensions of the mountedoptical sensor 114, and attributes of the sanding head 120 including:dimensions of sanding head 120; a geometry 123 of the sanding pad 121(e.g., area, diameter, flat contour, concave contour, convex contour) ofa currently installed sanding pad 121; a grit 122 of the currentlyinstalled sanding pad 121; a compliance 126 of the backing 125; and asanding pad wear model defining a pad wear 127.

In one variation, wherein the robotic system includes a linear actuator118, the tool profile further includes: linear actuator 118 dimensions;and a linear actuator 118 extension range.

The controller 115 can access the tool profile to retrieve attributes ofthe tool head, such as the geometry 123 of the sanding pad 121 or grit122 of the sanding pad 121, to calculate contact area and/or targetforce when defining keypoints or toolpaths. Additionally, the roboticsystem accesses the tool profile to retrieve dimensions of the endeffector 112 and connected components to model potential collisionsbetween the end effector 112 and the part surface or elements of thepart.

5. Part Loading, Operator Profile, and Part Processing Profile

In one implementation, prior to initiating a work cycle, an operator:loads a first part onto a first part carrier; arranges the first partcarrier supporting the first part in the work zone; and fixes the firstpart carrier in position within the work zone by engaging a set oflocking casters on the first part carrier.

Following the conclusion of the surface processing procedure, theoperator disengages the set of locking casters on the part carrier andremoving the part carrier and finished part from the work area.

5.1 Operator Profile

In one implementation, the robotic system includes an operator profiledefining the operator's default preference settings for the roboticsystem, including: a nominal traversal speed (e.g., one foot per second,one inch per second); a nominal toolpath pattern; a nominal sanding head120 dwell time; and/or a nominal material removal depth. Generally, theoperator profile is preloaded onto the robotic system prior to ascanning period. In one variation, the operator can manually enter datainto the robotic system via a user terminal to generate the operatorprofile.

In another variation, the operator profile defines a nominal traversalspeed range defined by a maximum traversal speed and a minimum traversalspeed.

In another variation, the operator can select one or multiplepreferences of the operator profile to override parameters of the partprocessing profile.

For example, the controller 115 can apply different operator preferencesin subsequent work cycles. The controller 115 retrieves aboustrophedonic raster pattern from a first operator profile associatedwith a first operator operating the robotic system during the first scancycle.

The robotic system can then apply a second set of operator preferencesof a second operator by: receiving a second part within the work zoneand accessing a second operator profile associated with a secondoperator. The robotic system can then, during a scan cycle of a secondwork cycle corresponding to the second part: autonomously manipulate therobotic system to move the optical sensor 114 across the second part;and, at the optical sensor 114, capture a second set of optical imagesdepicting the second part. the controller 115 then assembles the secondset of optical images into a second part model representing the secondpart.

The controller 115 then: characterizes surface contours within thesecond part model; detects a first region within the second part modelexhibiting a surface contour accessible to the sanding head 120 based onthe set of tool characteristics; and detects a second region within thesecond part model exhibiting a surface contour inaccessible to thesanding head 120 based on the set of tool characteristics.

The robotic system then retrieves a perpendicular double passboustrophedonic raster pattern from the second operator profiledefining: a first sequence of raster legs in a first orientation andoffset by a pitch distance less than the width of the sanding head 120;a second sequence of raster legs in a second orientation and connectingthe third sequence of raster legs; a third sequence of raster legs in athird orientation perpendicular to the first orientation and offset bythe pitch distance less than the width of the sanding head 120; and afourth sequence of raster legs in a fourth orientation and connectingthe third sequence of raster legs. The robotic system then projects theperpendicular double pass boustrophedonic raster pattern onto the secondpart model.

The robotic system then, for each keypoint in a second set of keypoints:defines a position of the sanding head 120 on the second part; defines asecond orientation of the sanding head 120 on the second part; defines atarget force value of the sanding head 120 on the second part; andassembles the second set of keypoints into a toolpath, following theperpendicular double pass boustrophedonic raster pattern, at localdensities proportional to local radii of surface contours within thefirst region within the second part model, for execution by the roboticsystem.

Therefore, the robotic system can retrieve default preferences, such astoolpath patterns or nominal translation speeds from the operatorprofile to inform the process protocol applied to a part. The operatorprofile can override other parameter inputs to limit the actions of therobotic system, such as assigning a default translation speed of thesanding head 120 thereby limiting the maximum translation speed of therobotic system, or setting a default toolpath pattern rather thancalculating a custom toolpath during each work cycle.

5.2 Part Processing Profile

In one implementation, the controller 115 stores a part processingprofile defining the parameters of a particular surface process on aparticular part composed of a particular material. The part processingprofile is divided into two sub-profiles: a process protocolsub-profile, defining parameters of the process protocol executable bythe robotic system; and a part sub-profile, defining the characteristicsof the part and the properties of the material from which the part isconstructed.

In this implementation, part processing profiles are assembled fromvarious sub-profiles to generate a part processing profile defining aprocess protocol unique to a particular part composed of a particularmaterial. In one variation, the part processing profile includes onlythe process protocol sub-profile, defining a process protocol for anypart.

Part processing profiles can be pre-loaded onto the robotic system,selectable for use by an operator. Additionally or alternatively thepart processing profile or a sub-profile can be generated from datamanually entered by the operator.

5.2.1 Processing Protocol Sub-Profile

The process protocol sub-profile defines: a set of properties of therobotic system or system components (e.g., grit 122 of sanding pad 121,geometry 123 of the sanding pad 121, and compliance 126 of the backing125) necessary to execute a particular process protocol, and/or a set ofexecution parameters governing actions performed by the robotic systemwhile executing the process protocol, such as toolpath pattern, sandinghead 120 traversal speed, and nominal target force exerted by a sandinghead 120 on the part. The processing protocol profile can additionallyinclude effect values related to the set of properties or executionparameters (e.g., material removal depth, material removal rate) derivedfrom the set of properties and execution parameters. Alternatively, theeffect value can be set by an operator. In response, the controller 115automatically adjusts the set of properties and execution parameters toproduce the effect value set by the operator.

A particular surface process can define: a process for stripping paint;a process for preparing a primer coat to receive a paint coat; and/or aprocess for buffing a final paint coat.

For example, the processing protocol profile can define a surfaceprocess corresponding to stripping paint, including: a coarse grit 122;a high target force; a fast traversal speed; and a high material removaldepth.

In another example, the processing protocol profile can define a surfaceprocess corresponding to preparing a primer coat to receive paint,including: a moderately coarse grit 122; a moderate target force; amoderate traversal speed; and a low material removal depth.

In yet another example, a processing protocol profile can define asurface process corresponding to buffing a coat of paint, including: avery fine grit 122; a low target force; a low traversal speed; and amaterial removal depth of zero.

The processing protocol profile defines the robotic system propertiesand execution parameters required to execute a particular processprotocol to achieve a surface process result on a part.

5.2.2 Part Sub-Profile

The part sub-profile includes attributes of a particular part typenecessary to determine the maximum force applicable to a given area ofthe part without causing damage to the part or the robotic systemincluding: a nominal curvature of the part; a material thickness; acoating type (e.g., paint to be striped, primer, bare material, finishedpaint to be buffed, clear coat to be polished); a coating thickness; acoating hardness; a part material type (e.g., steel, aluminum,fiberglass); a part material hardness; and an edge processing preference(i.e., avoid edges, process edges lightly).

The part profile can further include a force model, accessible by thecontroller 115 to calculate the nominal maximum force that can beexerted on the part surface by the robotic system without damage to thepart or the robotic system, based on curvature, material thickness,coating thickness and/or coating hardness.

For example: the controller 115 can access a hardness of a coating onthe part from the part sub-profile of the part loaded in the work zone;and define the set of target force values along the toolpathproportional to the hardness of the coating on the part.

In another example: the controller 115 can apply different partprocessing profiles to parts loaded into the work zone. The controller115 can apply a first part processing profile to a first part by:accessing a part stripping profile assigned to the first part andspecifying: a material removal depth; and a grit 122 specification of asanding pad 121 applied to the sanding head 120. The controller 115 thendefines the first set of target force values proportional to the firstmaterial removal depth and inversely proportional to the first grit 122specification.

The controller 115 can apply a second part processing profile to asecond part by receiving a second part within the work zone andaccessing a paint preparation profile assigned to the second part andspecifying: a second material removal depth; and a second grit 122specification, less than the first grit 122 specification, of a secondsanding pad 121 applied to the sanding head 120.

The controller 115 then, during a second scan cycle: manipulates therobotic system to move the optical sensor 114 across the second part;and, at the optical sensor 114, captures a second set of optical imagesdepicting the second part.

The controller 115 then: assembles the second set of optical images intoa second part model representing the second part; characterizes surfacecontours within the second part model; detects a first region within thesecond part model exhibiting a surface contour accessible to the sandinghead 120 based on the set of tool characteristics; detects a secondregion within the first part model exhibiting a surface contourinaccessible to the sanding head 120 based on the set of toolcharacteristics; and defines a set of keypoints on the first regionwithin the second part model. The controller 115, for each keypoint inthe second set of keypoints: defines a position of the sanding head 120on the second part; and defines an orientation of the sanding head 120on the second part.

The controller 115 then and defines a second target force value of thesanding head 120 on the second part: proportional to the second materialremoval depth; and inversely proportional to the second grit 122specification. The controller 115 finally assembles the second set ofkeypoints into a toolpath for execution by the robotic system.

In another example, the operator loads a part into the work zonedefining a steel automobile hood of a nominal thickness of one-sixteenthof an inch. The operator selects a part processing profile correspondingto stripping paint from the steel automobile hood defining: a coarsegrit 122 of sanding pad 121; a toolpath pattern defining a singleboustrophedonic pass over the part surface; a slow sanding head 120traversal speed, resulting in a high dwell time; and a large materialremoval depth, a nominal part curvature with a contour radius greaterthan twelve feet, a nominal part geometry 123 representing aquadrilateral, a nominal part thickness greater than one-sixteenth of aninch, and a nominal maximum force for steel of one-half inch thickness.

The controller 115 retrieves the parameters from the part processingprofile to calculate a target force to achieve the desired finish ofbare steel (i.e., paint has been stripped) along the tool path based onthe parameters of the part processing profile for stripping paint fromthe steel automobile hood.

In another example, the operator loads a part into the work zonedefining a painted steel automobile hood. The operator selects a partprocessing profile corresponding to buffing paint including a set ofprocessing parameters defining: a very fine grit 122; a toolpath patterndefining a perpendicular double-pass boustrophedonic raster pattern; aslow sanding head 120 traversal speed, resulting in a high dwell time; asmall material removal depth; a coating type (i.e., finished paint to bebuffed); and a coating hardness.

The controller 115 retrieves the set of parameters from the partprocessing profile to calculate a target force less than a maximum forcefor finished paint defined in the part sub-profile, along the tool pathto achieve the desired finish of buffed paint along the tool path.

In yet another example, the operator loads a part into the work zonedefining a fiberglass wind turbine blade of a wall thickness of one-halfmillimeter. The operator selects a part processing profile correspondingto preparing a primer coat on the surface of the fiberglass wind turbineblade to receive paint including a set of processing parametersdefining: a moderately coarse grit 122; a toolpath pattern defining asingle raster pass over the part surface; a fast sanding head 120traversal speed, resulting in a low dwell time; a small material removaldepth; a nominal part curvature with a contour radius greater than twofeet; a nominal part geometry 123 representing a contoured airfoil; anominal part wall thickness greater than one-half millimeter; and anominal maximum force for fiberglass of one-half millimeter thickness.

The robotic system retrieves the parameters from the part processingprofile and calculates a target force, less than the nominal maximumforce for fiberglass of one-eighth inch thickness, to achieve thedesired finish of prepared primer along the tool path.

Therefore, the part processing profile contains the parameters of thepart and the process parameters to effectuate surface processing of aparticular part such as stripping paint, preparing a primer coating toreceive a paint coating, and/or to buff a paint coating.

The part processing profile can be stored locally at the robotic systemto be readily selected by an operator to process multiple instances ofsimilar parts. Additionally, the set of pre-loaded part processingprofiles enables a single operator to select from an array of partprocessing profiles to perform a variety of surface processes on avariety of parts exhibiting a variety of material properties on the samerobotic system. Furthermore, the set of pre-loaded part processingprofiles enables a single operator to process a single part through aseries of surface processes on the same robotic system.

The operator profile enables the operator to set default parameters orpreferences for individual processes, or for all processes performed onthe robotic system, such as a uniform tool path pattern across allprocesses, or a uniform translation speed of the sanding head 120.

6. Part Scanning

In one implementation as shown in FIGS. 1, 2 and 4 , the robotic systemexecutes a first, rapid, low-resolution scan of the work zone of thepart loaded into the work zone by sweeping the optical sensor 114 acrossthe work zone at a first distance from the floor of the work zone, tocollect a set of images depicting the work zone and the part loadedtherein. In particular, the robotic manipulator 110 translates theoptical sensor 114, mounted to the end effector 112, to the maximumdimensions and/or to the maximum dimensions of the work zone. Thecontroller 115 then assembles the set of images into a lower-resolutionmodel of the part to determine the nominal geometry 123 and dimensionsof the part. In one variation, the robotic system translates the opticalsensor 114 to a maximum height above the center of the work zone andcaptures a single depth map depicting the part. The robotic system thenassembles the lower-resolution part model from the single image todetect part geometry 123 and dimensions.

The robotic system then executes a second, higher-resolution scan of thepart to determine part features, such as part contour, coating, internaledges or features, and boundary edges of the part. The robotic systemassembles a scan pattern from the first scan by: segmenting thelow-resolution part model by the area of the field of view of theoptical sensor 114 at a nominal scan distance from the part (i.e.,twelve inches); projecting a set of scan points onto the surface of thefirst scan; and defining an orientation of the focal axis of the opticalsensor 114 approximately normal to the part surface.

The robotic system executes the second scan by locating a focal axis ofthe optical sensor 114 approximately normal to the part while maintainthe optical sensor 114 at the nominal scan distance and collecting a setof images depicting the part. The controller 115 then assembles the setof images into a higher-resolution part model.

For example, the robotic system can execute the first scan to quicklydetermine the part boundaries and generate a nominal scan path during asetup period preceding the first scan period by: locating the opticalsensor 114 over the work zone at a first distance from the first part;capturing a first optical image of the work zone depicting the firstpart at a first resolution; detecting a first geometry 123 of the firstpart within the work zone based on a first set of features extractedfrom the first optical image; and defining a scan path, at a seconddistance from the first part less than the first distance, based on thefirst geometry 123 of the first part within the work zone. The roboticsystem can then execute the second scan to capture a high-resolutionrepresentation of the part by: autonomously executing the scan path totranslate the optical sensor 114 over the first part at the seconddistance from the first part; and capturing the first set of opticalimages depicting the first part at a second resolution greater than thefirst resolution.

Therefore, the robotic system can efficiently execute a first,lower-resolution scan to detect the geometry 123 and dimensions of thepart with a low dimensional accuracy, assemble a lower-resolution partmodel, and segment the low-resolution part model into regions scannableby the optical sensor 114 positioned at a closer, nominal distanceduring a second, higher-resolution scan. The robotic system can thenexecute the higher-resolution scan to detect part features—such assurface contours, coatings, internal edges and features, and boundaryedges of the part—at greater dimensional accuracy sufficient to definethe toolpath within a spatial tolerance (e.g., +/−0.25″) of the surfaceof the part and to define target force values along the toolpathpredicted to yield consistent material removal and/or surface qualitywhen executed by the robotic system.

7. Part Model

In one implementation as shown in FIGS. 1 2, 4-6, the controller 115assembles two-dimensional images, depth maps, stereoscopic images,and/or other optical data—collected by the robotic system via the set ofoptical sensor 114 s during the scan—into a three-dimensional part modelrepresenting surfaces of the part, such as within a spatial tolerance of+/−0.25″.

The controller 115 can derive surface contours from thethree-dimensional part model, such as by calculating a local radius ofcurvature at each pixel within the three-dimensional part model. Thecontroller 115 can also: characterize a surface contour with a negativelocal radius as a convex contour (e.g., if the center of a spheretangent to the part model at a pixel falls below the part surface); andcharacterize a surface contour with a positive local radius as a convexcontour (e.g., if the center of a sphere tangent to the part model at apixel falls above the part surface), Furthermore, the controller 115 canimplement edge detection techniques to detect boundary edges of the partwithin the three-dimensional part model.

In one variation, the controller 115: detects color characteristics(e.g., color intensity, reflectivity) of the surface of the part model;predicts a surface type of the part (e.g., primer, paint, metal,fiberglass) based on these color characteristics; selects a partprocessing profile based on the surface type; and/or delineates segmentsof the part model between regions exhibiting distinct colorcharacteristics (e.g., high reflectivity indicating paint versus lowreflectivity indicating primer or filler).

Therefore, the controller 115 can assemble a part model from the set ofimages collected by the robotic system during the scan cycle to definethe boundaries of the part and the contours of the part, therebyproducing a virtual representation of the part. The controller 115 thencalculates a toolpath and parameters for autonomously processing thepart based on this part model.

7.1 Part Model Segmentation

Generally, the controller 115 segments the part model into a set oftarget zones that the robotic manipulator 110 will process with thesanding head 120 and a set of exclusion zones inaccessible or unsuitablefor the robotic manipulator 110 to process with the sanding head 120,based on the capabilities of the robotic system and the desired surfacefinish.

7.1.1 Target Zones

In one implementation as shown in FIGS. 1 and 5 , the controller 115segments the part model into a target zone by identifying a pixel withinthe edges of the part. The controller 115 then identifies the localcurvature radius at the pixel as a concave curvature, more than a firstthreshold radius, and/or identifies the local curvature radius at thepixel as a convex curvature, more than a second threshold radius. Inresponse, the controller 115 assigns the pixel to a target zone in thepart model.

In another implementation, the controller 115 can access the toolcharacteristics to retrieve a geometry 123 of the sanding pad 121 and asanding head 120 compliance 126 of the backing 125. The controller 115calculates—based on the geometry 123 of the sanding pad 121 and sandinghead 120 compliance 126 of the backing 125—a first minimum contourradius of a surface contour, such that a threshold percentage of thesanding pad 121 area can make contact with the surface contour when anominal target force is applied, the target force retrieved from theoperator profile and/or the part processing profile.

In another implementation, the controller 115 segments the part modelinto a target zone by identifying a pixel exhibiting a contour radiusless than the first minimum contour radius, and assigning the pixel tothe target zone.

For example, the controller 115 accesses the tool characteristics toretrieve a first geometry 123 of the sanding pad 121 of six inches and acompliance 126 of the backing 125 of 25% (i.e., semi-rigid backing 125),and retrieves a nominal target force from the operator profile. Thecontroller 115 calculates the threshold percentage of the sanding pad121 area in contact with the part as 50%, based on the compliance 126 ofthe backing 125 and the nominal target force. The controller 115calculates the first minimum contour radius as ten feet based on thegeometry 123 of the sanding pad 121 the sanding head 120 compliance 126of the backing 125 and the nominal target force. The controller 115segments pixels with a local curvature radius of ten feet or greaterwithin a first target zone. The controller 115 then projects a firsttoolpath onto the target zone within the part model.

The controller 115 then accesses the tool characteristics to retrieve asecond geometry 123 of the sanding pad 121 of four inches and acompliance 126 of the backing 125 of 50% (i.e., semi-flexible backing125), and retrieves the nominal target force from the operator profile.The controller 115 calculates the threshold percentage of the sandingpad 121 area in contact with the part as 75%, based on the compliance126 of the backing 125 and the nominal target force. The controller 115calculates the first minimum contour radius as one foot based on thegeometry 123 of the sanding pad 121 and the compliance 126 of thebacking 125. The controller 115 segments pixels with a local curvatureradius of one foot or greater within a second target zone. Thecontroller 115 projects a second toolpath onto the second target zonewithin the part model.

The controller 115 then accesses the tool characteristics to retrieve athird geometry 123 of the sanding pad 121 of two inches and a compliance126 of the backing 125 of 25% (i.e., semi-rigid backing 125), andretrieves the nominal target force from the operator profile. Thecontroller 115 calculates the threshold percentage of the sanding pad121 area in contact with the part as 25%, based on the compliance 126 ofthe backing 125 and the nominal target force. The controller 115calculates the first minimum contour radius as one inch based on thegeometry 123 of the sanding pad 121 and the compliance 126 of thebacking 125. The controller 115 segments pixels with a local curvatureradius of one inch or greater within a third target zone. The controller115 projects a third toolpath onto the third target zone within the partmodel.

The controller 115 then sequences the first toolpath, the secondtoolpath, and the third toolpath into a single processing cycle,including tool change events between the conclusion of the firsttoolpath and the commencement of the second toolpath, and between theconclusion of the second toolpath and the commencement of the thirdtoolpath, to process all target zones of the part.

In one variation of this example, the robotic system includes anautomated tool changer, configured to receive a first sanding head 120from the end effector 112, and dispense a second sanding head 120 to theend effector 112, the end effector 112 configured to selectivelydisengage the first sanding head 120 and selectively engage the secondsanding head 120. The robotic system engages the automated tool changerto exchange sanding head 120 s of different sizes when transitioningfrom the first toolpath to the second toolpath, and from the secondtoolpath to the third toolpath.

In another variation of this example, in response to conclusion of thefirst toolpath, the controller 115 generates and transmits a prompt tothe operator to manually change the first sanding head 120. Following amanual exchange of the first sanding head 120 for a second sanding head120, the robotic system continues along the second toolpath.

Thus, the robotic system can sequence the first toolpath, the secondtoolpath, and the third toolpath to process all target zones on the partin the shortest duration of time by covering the greatest area of thepart with a sanding head 120 of greatest geometry 123, and progressivelyreducing the geometry 123 of sanding pad 121 to process contours ofsmaller and smaller radii.

Therefore, the robotic system can segment the part model into targetzones wherein the robotic system can process the part. The roboticsystem can detect the local contour radius at locations on the part andcompare the local contour radius to the size of the sanding head 120 andthe sanding head 120 compliance 126 to identify zones of the partwherein the sanding head 120 can access the part surface andautonomously segment the target zone from the remainder of the part.

7.1.2 Exclusion Zones

In one implementation as shown in FIGS. 1 and 5 , the controller 115segments the part model into an exclusion zone by: identifying a pixelwithin the edges of the part; and identifying the local curvature radiusat the pixel is a concave curvature less than a first threshold radiusand/or identifying the local curvature radius at the pixel is a convexcurvature less than a second threshold radius. In response, thecontroller 115 assigns the pixel to an exclusion zone in the part model.

In another implementation, the controller 115 can access the toolcharacteristics to: retrieve a geometry 123 of the sanding pad 121and/or a sanding head 120 compliance 126 of the backing 125 andcalculate a first minimum contour radius of a surface contour, based onthe geometry 123 of the sanding pad 121 and/or sanding head 120compliance 126 of the backing 125, that a threshold percentage of thesanding pad 121 area can make contact with the surface contour when anominal target force—retrieved from the operator profile and/or the partprocessing profile—is applied.

The controller 115 segments the part model into an exclusion zone byidentifying a pixel exhibiting a contour radius greater than the firstminimum contour radius and assigning the pixel to the exclusion zone.

In one example, the controller 115 can segment an exclusion zoneinaccessible to the sanding head 120 based on the properties of thesanding head 120 by: accessing a sanding pad 121 size; detecting thesecond region defining a concave contour; detecting a radius ofcurvature of the concave contour; and calculating a ratio of the sandingpad 121 size to the radius of curvature of the concave contour. Inresponse to the ratio exceeding a threshold value, the controller 115characterizes the second region as an exclusion zone. Additionally, thecontroller 115 can: further access a compliance 126 coefficient of acompliant backing 125; and calculate the threshold value based on thecompliance 126 coefficient.

In another implementation, the controller 115 can segments the partmodel into an exclusion zone by: identifying different minimum curvatureradii for different curvature types. For example, the controller 115 canidentify a pixel within the boundary edges of the part and identify thelocal curvature at the pixel as a concave curvature. The controller 115can identify the concave curvature radius as less than a first thresholdradius, and in response assign the pixel to the exclusion zone.Alternatively, the controller 115 can identify a pixel within theboundary edges of the part and identify the local curvature at the pixelas a convex curvature. The controller 115 can identify the convexcurvature radius as less than a second threshold radius—different fromthe first threshold radius—and in response assign the pixel to theexclusion zone.

In yet another implementation, the controller 115 can detect a varietyof edges in the part model. The controller 115 can implement edgedetection techniques to detect: a boundary part edge defining the partlimit; and an internal part edge defining a feature edge, such as theedge of a boss, relief, or hole in the surface.

Additionally, the controller 115 can analyze the set of images to detectmasking tape edges on the part. The controller 115 can segment the partmodel into an exclusion zone by: identifying a pixel within an areabounded by a set of edges of the part; and assigning the pixel to anexclusion zone in the part model.

In another example, the controller 115 detects a region within the partmodel inaccessible to the sanding head 120 by: detecting a set of edgeson the first part model; defining the region on the part model boundedby the set of edges as an exclusion zone in the part model; and definingthe set of keypoints on the part model outside of the exclusion zone.

In another example, the controller 115 can detect the set of edges onthe part model and segment an exclusion zone by: detecting masking tapeon a surface contour of the part; detecting a first edge of the maskingtape delineating a target zone of the first region from the exclusionzone; and defining the region on the part model bounded by the firstedge of the masking tape as an exclusion zone.

In yet another example, the controller 115 can detect a first regionrepresenting a target zone within the part model by: detecting a regionof a first color on the part in the part model; defining the firstregion on the first part model as a target zone in the first part model;detecting an area of a second color in the part model, the first colordifferent from the second color; and defining the set of keypointswithin the first region of the part model representing the target zone.

In one variation of this implementation, the controller 115 furthersegments the part model into an exclusion zone by: identifying a pixelwithin a minimum distance of an edge of the part; and assigning thepixel to an exclusion zone in the part model.

In another variation of this implementation, the controller 115 canannotate the three-dimensional model with the exclusion zone and presentthe three-dimensional model to the operator to confirm the exclusionzone prior to initiation of the processing cycle.

For example, the controller 115 can represent target zones and executionzones within a three-dimensional model and request confirmation from anoperator by: detecting a set of edges in the three-dimensional model;defining the region on the part model within the set of edges as anexclusion zone in the part model; and annotating the three-dimensionalmodel with a virtual representation of the exclusion zone, presentingthe three-dimensional model annotated with the virtual representation ofthe exclusion zone to the operator; and prompting the operator toconfirm the exclusion zone on the three-dimensional model.

In another implementation, the controller 115 can access the toolcharacteristics to retrieve the dimensions of the sanding head 120 andend effector 112. The controller 115 generates an end effector 112simulator, based on the dimensions of the sanding head 120 and endeffector 112, to predict collisions between the end effector 112 (and/orother elements of the robotic manipulator 110) and elements of the part.

For example, the controller 115 identifies an overhang at a firstkeypoint along the toolpath and accesses the end effector 112 simulatorto calculates a target position and orientation of the end effector 112at the first keypoint, proximal the overhang. The end effector 112simulator indicates a collision between the end effector 112 and theoverhang based on the dimensions of the sanding head 120 and endeffector 112 and the calculated target position and orientation of theend effector 112. In response, the controller 115 assigns the firstkeypoint to the exclusion zone.

Therefore, the robotic system can autonomously segment the part modelinto exclusion zones, that are either inaccessible to or undesirable forthe robotic manipulator no to process with the sanding head 120 based onthe capabilities of the robotic system and the desired surface finish.The robotic system can also segment areas of the part that may bedamaged by the sanding head 120 or by the parameters of a particularprocess, such as low-radius concave or convex contours, which can bedamaged or ground away during an aggressive paint stripping cycle with acoarse grit 122. The robotic system can also model the path of the endeffector 112 and predict a location of a potential collision and segmentthe area as an exclusion inaccessible to the sanding head 120.

8. Toolpath

Generally, for each target zone in the part model, the controller 115projects a toolpath including a set of keypoints onto the target zone,with a toolpath pattern retrieved from the operator profile.

In one implementation as shown in FIGS. 2 and 3 , the controller 11Sgenerates a toolpath by projecting a boustrophedonic raster pattern,defined by the operator profile, onto the target zone, and projects aset of keypoints onto the boustrophedonic raster pattern at a fixedinterval.

For example, the controller 115 can define the first set of keypoints onthe first region within the first part model by: retrieving aboustrophedonic raster pattern defining a first sequence of raster legsin a first orientation and offset by a pitch distance less than a widthof the sanding head 120 and a second sequence of raster legs in a secondorientation and connecting the first sequence of raster legs. Thecontroller 115 then: projects the boustrophedonic raster pattern ontothe first region within the first part model; and defines the first setof keypoints along the boustrophedonic raster pattern at local densitiesproportional to local radii of surface contours within the first regionwithin the first part model.

In one variation of the example implementation, the controller 115projects the set of keypoints onto the boustrophedonic raster patterndefined by the operator profile, onto the target zone at an intervalinversely proportional to the local curvature radius at each keypoint(i.e., a smaller local curvature radius results in a greater density ofkeypoints in the toolpath.)

For example, the controller 115 can: characterize surface contourswithin the first part model by detecting local radii of curvature of thesurface contour within discrete areas of the part model; and define thefirst set of keypoints on the first region within the first part modelby projecting keypoints onto the part model at densities inverselyproportional to local radii of curvature. By increasing the density ofkeypoints inversely to local radii of curvature, the controller 115produces a more detailed segment of the toolpath for tighter control ofthe sanding head 120 through tight contours.

8.1 Target Force Values by Curvature

Generally, the controller 115 populates each keypoint with atranslational (e.g., (x,y,z)) position and a rotational (e.g., pitch,yaw, and roll) orientation, such as within machine coordinates of therobotic system. The controller 115 also: derives a target force (orpressure) value for each keypoint; and annotates each keypoint with itstarget force value. (Alternatively, the controller 115 can segment thetoolpath into regions and implement methods and techniques describedherein to assign target force values to individual regions of thetoolpath. Additionally or alternatively, the controller 115 can segmentthe toolpath into groups of keypoints and implement methods andtechniques described herein to assign target force values to individualgroups of keypoints along the toolpath.)

In one implementation as shown in FIG. 5 , for a first keypoint, thecontroller 115: retrieves (e.g., reads, extracts) a local curvatureradius of the part at the first keypoint from the part model; accessesthe set of tool characteristics to retrieve the geometry 123 of thesanding pad 121 and the compliance 126 of the backing 125; projects thearea of the sanding pad 121 onto the part; calculates a contact areabetween sanding pad 121 and the part surface based on the sanding pad121 area, the compliance 126 of the backing 125, and the local curvatureradius when a) the sanding head 120 is positioned such that the sandingpad 121 is centered at the first keypoint, b) the axis of the sandinghead 120 is oriented normal to the part surface at the first keypoint,and c) the sanding pad 121 is in contact with the part surface; andcalculates a target force value at the first keypoint proportional tothe contact area between the sanding pad 121 and the part surface.Accordingly, the controller 115 can assign a lower target force to thefirst keypoint for a lower estimated sanding pad 121 contact area aroundthe first keypoint and a higher target force to the first keypoint for ahigher estimated sanding pad 121 contact area around the first keypointin order to achieve a consistent or target sanding pressure between thesanding pad 121 and the entire surface of the part, and thus achieveconsistent material removal and high surface quality uniformity.

In one variation, the controller 115 calculates a target force for thefirst keypoint directly from local part curvature by: extracting a localradius of curvature of the part at the first keypoint; retrieving apredefined grit 122 specification of the sanding pad 121, traversalspeed, and/or the part processing profile for the part; and insertingthe local radius of curvature and the processing values into apredefined model to convert this local curvature radius into the targetforce for the first keypoint.

8.2 Target Force Values by Edge Proximity

In another implementation in which the first keypoint is locatedproximal an edge of the target zone as shown in FIG. 5 , the controller115: projects the area of the sanding pad 121 onto the part; calculatesa contact area between sanding pad 121 and the part surface based on thesanding pad 121 area, and location of the keypoint when the sanding head120 is positioned such that a) a first region of the sanding pad 121 isin contact with the part surface within the target zone, b) and a secondregion of the sanding pad 121 extends beyond the part boundary edge whenthe sanding head 120 is centered at the first the first keypoint, and c)the axis of the sanding head 120 is oriented normal to the part surfaceat the first keypoint; and defines the target force proportional to thefirst region of the sanding pad 121, in contact with the part surfacewithin the boundary of the target zone. For example, the controller 115can calculate a first contact area for each region of the first toolpathby, for each region of the first toolpath: calculating an intersectionof the geometry 123 of the sanding head 120, projected onto the regionin the part model, and the part model; and calculating a first contactarea for the region based on the intersection.

8.3 Target Force Values by Contact Area

In one implementation as shown in FIGS. 2-3 and 5-6 , the controller 115calculates a target force at a first keypoint in the toolpath by:retrieving a nominal translation speed, (i.e., one foot per second) fromthe operator profile; retrieving the geometry 123 of the sanding pad 121and the compliance 126 of the backing 125; projecting the area of thesanding pad 121 onto the part; calculating a contact area between thesanding pad 121 and the part surface based on the sanding pad 121 area,the compliance 126 of the backing 125, and the local curvature radiuswhen the sanding pad 121 is centered at the first keypoint and the axisof the sanding head 120 is oriented normal to the part surface at thefirst keypoint; and calculating a target force value at the firstkeypoint proportional to the contact area between the sanding pad 121and the part surface and proportional to the nominal translation speed(i.e., faster translation speed results in a higher target force).

For example, the controller 115 can: retrieve a nominal translationspeed of the sanding head 120 for a region of the toolpath; define atarget force value of the sanding head 120 on the part proximal theregion proportional to a first contact area between the sanding head 120and the part surface; and proportional to the nominal translation speed.The controller 115 can: read a sequence of force values from the sensorincluding a force sensor 116 coupled to the sanding hand; and deviatefrom the toolpath to maintain the sequence of force values within thethreshold difference of the set of target force values.

8.4 Target Force Values by Pressure

In another example, the robotic system accesses the operator profile toretrieve a nominal traversal speed of one foot per second and accessesthe part processing profile to retrieve a maximum pressure for the part.Generally, as the sanding head 120 translates at the nominal traversalspeed along the toolpath and encounters a convex region of the surfaceexhibiting a decreasing radius of curvature, the contact area of thesanding head 120 on the part decreases, such as proportional to thedecreasing radius of curvature of the part. If the robotic systemmaintains a consistent force application on this part over this regionof the part, the pressure exerted by the sanding head 120 on the partmay increase, thereby yielding increased material removal from the part.Therefore, in order to maintain a consistent pressure exerted on thepart and/or to maintain this pressure below the maximum pressure, thecontroller 115 can: characterize a contact area between the sand pad thepart across this region of the part; and assign decreasing target forcevalues along this segment of the toolpath.

Similarly, as the sanding head 120 moves across a region of the partcharacterized by increased radius of curvature, the contact area of thesanding pad 121 increases and the pressure applied by the sanding head120 decreases. Accordingly, the controller 115 can assign increasingtarget force values along this segment of the toolpath.

In another implementation, the controller 115 calculates a targetpressure on the part surface inversely proportional to the contact areaof the sanding head 120 on the part and proportional to the targetforce. The robotic system modulates the target force based on the localsurface contour radius, and therefore the contact area of the sandinghead 120, to achieve the target pressure across the part.

In one variation, the controller 115 retrieves a maximum pressure forthe part from the part processing profile, accesses the sanding pad 121size, and sets the target force such that the pressure exerted by thesanding pad 121 on the part does not exceed the maximum part pressure.

In one example, the controller 115 accesses a maximum applied pressurefor the part and, for each region of the first toolpath: calculates amaximum force for the region based on the maximum applied pressure and afirst contact area between the first sanding head 120 and the partsurface proximal the region; and defines a target force value of thesanding head 120 on the part less than the maximum force.

8.5 Target Force Values by Geometry

In another implementation, the controller 115 calculates a targettranslation speed at a first keypoint by: retrieving a target force ofthe sanding head 120 against the part and a maximal nominal force forthe part from the part processing profile; calculating a contact areabetween the sanding pad 121 and the part based on geometry 123 of thesanding pad 121 and compliance 126 of the backing 125; and calculating atarget translation speed at the first keypoint proportional to thecontact area between the sanding pad 121 and the part surface andproportional to the target force. (i.e., lower contact area—due to smallradius of curvature at the keypoint—results in higher translation speedas to not exceed the maximum nominal force for the part surface).

In one example, the controller 115 can retrieve the set of nominalprocessing parameters by retrieving a nominal applied sanding head 120force and, for each region of the toolpath, assigning the nominalapplied sanding head 120 force. The controller 115 can then, for eachregion of the toolpath, assign a target sanding head 120 translationalspeed of the sanding head 120 on the part inversely proportional to acontact area between the sanding head 120 and the part surface proximalthe region; and proportional to the nominal applied sanding head 120force. The controller 115 can then move the sanding head 120 along thetoolpath according to target sanding head 120 translational speedsassigned to regions of the toolpath. The controller 115 reads a sequenceof force values from the sensor including a force sensor 116 coupled tothe sanding hand; and deviates from the toolpath to maintain thesequence of force values within the threshold difference of the set oftarget force values.

8.6 Target Force Values by Grit

In another implementation, the controller 115 defines the target forceproportional to the grit 122 specification of the sanding head 120 toachieve a target material removal depth on the part.

For example, the controller 115 can access the set of toolcharacteristics of the sanding head 120 by accessing a first grit 122specification of a first sanding pad 121 applied to the sanding head120. The controller 115 then: accesses a first material removal depthrange for the first part; and accesses a first tool translation speedpreference. The controller 115 can then define the first set of targetforce values: proportional to the material removal depth range;proportional to first tool translation speed preference; and inverselyproportional to the first grit 122 specification. The controller 115then controls the robotic system to move the sanding head 120 along thefirst sequence of positions and orientations according to the first tooltranslation speed preference.

The controller 115 can then: access a second grit 122 specification of asanding pad 121 applied to the sanding head 120; and access a secondfinish profile defining a second tool translation speed preference, anda second sanding force preference. The controller 115 then: defines asecond traversal speed along the toolpath based on the second tooltranslation speed preference and the second grit 122 specification; anddefines a second set of preference force values based on the secondsanding force preference and the second grit 122 specification.

Later, the robotic system: moves the sanding head 120 along the sequenceof positions and orientations, defined by the set of keypoints, relativeto the first part, at the second traversal speed; reads a secondsequence of forces values from the force sensor 116 in the roboticsystem; interpolates a second set of target force values along thetoolpath based on the second set of preference force values; andselectively adjusting positions of the end effector 112 relative to thepart to maintain the sequence of force values within a thresholddifference of the second set of preference force values.

In a similar variation, the controller 115 calculates a target forceexerted by the sanding head 120 on the part during execution of thetoolpath to affect material removal from the part surface based on thematerial properties of the part (e.g., hardness), the toolcharacteristics of the sanding head 120 (e.g., grit 122 of sanding pad121), and action parameters of the robotic system (e.g., sanding head120 traversal speed.)

8.7 Processing Parameters by Sanding Torque

In another implementation, the controller 115 calculates a target torqueon the axis of the sanding head 120 at a first keypoint by: retrieving anominal translation speed, (i.e., one foot per second) from the operatorprofile; calculating a contact area between sanding pad 121 and the partbased on geometry 123 of the sanding pad 121 and compliance 126 of thebacking 125; and calculating a target torque at the first keypointproportional to the contact area between the sanding pad 121 and thepart surface and proportional to the nominal translation speed (i.e.,faster translation speed results in a higher target torque.)

For example: the robotic manipulator 110 includes a torque sensorcoupled to the sanding head 120 and configured to output signalsrepresenting torque values between a sanding pad 121 on the sanding head120 and local areas of the part in contact with the sanding pad 121. Thecontroller 115 defines target sanding torques across the partproportional to radii of local surface contours represented in the partmodel. The robotic manipulator 110 is configured to modulate a sandingpad 121 speed of the sanding head 120 to align torque values, betweenthe sanding pad 121 and local areas of the part, to the target sandingtorques while navigating the sanding head 120 along the toolpath.

Therefore, the robotic system can calculate the target force of thesanding head 120 on a part based on one or a multiple of several partparameters and/or system parameters to achieve the target force withhigh accuracy for a variety of different part geometries, materials,and/or processing protocols. The robotic system can also vary systemparameters during execution of the toolpath in real time, such as thesanding head 120 translation speed, in response to fluctuations in thedetected applied force, to achieve the target force.

8.8 Translation Speed Modulation

In another implementation, the robotic system modulates the forceexerted by the sanding head 120 and the translation speed of the sandinghead 120 for each keypoint in the set of keypoints.

For a first keypoint, the robotic system: calculates a force andtranslation speed combination at the first keypoint based on the partprocessing profile, local part contour radius at the keypoint, sandingpad 121 contact area, and/or grit 122 specification, to nominallyachieve the target force exerted on the part surface by the sanding head120, as defined in the part processing profile. The controller 115interpolates a force and translation speed combination between the firstkeypoint and a second keypoint in the toolpath. The controller 115repeats the foregoing process for each keypoint in the set of keypointsand assembles the keypoints into a tool path with a minimum durationthat maintains the force exerted on the part less than the maximum forcefor the part as defined in the part processing profile.

For example: the controller 115 accesses the set of tool characteristicsof the sanding head 120 to access a grit 122 specification of thesanding pad 121 and retrieve a minimum material removal depth for thepart and a maximum toolpath execution duration. The controller 115 thendefines the target execution value for each region of the firsttoolpath, for each region of the first toolpath by assigning a targettranslation speed to the region inversely proportional to the maximumtoolpath execution duration. The controller 115 further assigns a targetforce value to the region: proportional to a contact area of the sandinghead 120 on the part proximal the region; inversely proportional to thegrit 122 specification of the sanding pad 121; proportional to theminimum material removal depth; and proportional to the targettranslation speed.

The robotic system then: moves the sanding head 120 along the toolpathaccording to target sanding head 120 translational speeds assigned toregions of the toolpath; reads a sequence of force values from thesensor including a force sensor 116 coupled to the sanding hand; anddeviates from the toolpath to maintain the sequence of force valueswithin the threshold difference of the set of target force values.

Alternatively, the controller 115 can assemble the set of keypoints,defined by the set of force and translation speed combinations, into atool path that maintains the most consistent traversal speed, topreserve final pattern uniformity. Alternatively, the controller 115 canassemble the set of keypoints, into a tool path that maintains the mostconsistently achieves the target force exerted on the part less asdefined in the part processing profile. Alternatively, the controller115 can assemble the set of keypoints, into a tool path which exerts theminimum force to complete the surface finish process within a setduration (i.e., one hour). Alternatively, the controller 115 canassemble the set of keypoints, into a tool path which optimizes thefinish consistency across the part surface.

Therefore, the robotic system can modulate both translation speed of thesanding head 120 and exerted force on the part surface by the sandinghead 120 to assemble a particular toolpath to accomplish a particulargoal within the surface process.

In another example, the operator loads a truck tailgate exhibiting areaswith spilled truck bed liner and selects a paint stripping protocol witha maximum duration of one hour. The robotic system segments a zone ofthe part exhibiting truck bed liner in the toolpath and assigns a highertarget force and lower translation speed to the zone to increase dwelltime and therefore material removal depth of the hard truck bed liner.Elsewhere in the toolpath, the robotic system assigns a lower targetforce and a higher translation speed to reduce dwell time and materialremoval depth, as well as reduce overall process execution time.

Therefore, the robotic system can modulate the target force and thetranslation speed of the sanding head 120 to achieve a process result,as opposed to fixing target force and modulating translation speed orfixing translation speed and modulating force. Thereby the roboticsystem can efficiently process a part exhibiting highly variable surfacegeometry 123 or composition.

8.9 Other Keypoints

The robotic system can repeat the forgoing processes to calculate targetexecution values (e.g., target force, target translation speed, targetpressure) for each other keypoint, group of keypoints, or region definedon the part model. The controller 115 then assembles the positions,orientations, and target execution values of these keypoints into atoolpath, such as in the form of a software code file (e.g. a machinespecific programming language or G-code equivalent) definingtranslational positions and rotational orientations, target forces,sanding head 120 feed speeds, and/or sanding pad 121 rotation speeds.8.10 Keypoint Order

In one variation the controller 115 orders the keypoint in the toolpathbased on characteristics of corresponding regions of the part.

For example, the controller 115 can segment the part model or thetoolpath into a set of zones characterized by coating thickness, such asincluding: a first zone characterized by a first coating thickness; anda second zone characterized by a second coating thickness less than thefirst coating thickness. The controller 115 then: assigns a secondtarget force value—based on the second coating thickness—to a firstregion (e.g., a first group of keypoints) of the toolpath that fallswithin the first zone; assigns a second target force value—less than thefirst force value based on the second coating thickness—to a secondregion (e.g., a second group of keypoints) of the toolpath that fallswithin the second zone; and defines a processing order for the set ofregions of the toolpath such that the first region of the toolpathprecedes the second region of the toolpath based on the first coatingthickness exceeding the second coating thickness and such that thesanding pad 121 may strip more material from the thicker coating in thefirst region when fresh and then strip less material from the thinnercoating in the second region once worn.

Therefore, the controller 115 can generate a toolpath—executable by therobotic system—containing a sequence of keypoints: that define positionsand orientations of the sanding head 120; and that are annotated withprocess protocol parameters governing actions of the robotic systemwhile processing the part in order to achieve target results of aselected process protocol for the part.

8.1 Toolpath Visualization and Confirmation

In one variation, the controller 115 further: projects the toolpath ontothe part model (e.g., a three-dimensional model of the part); presentsthis annotated three-dimensional model to the operator; animates thetoolpath projection on the annotated three-dimensional model; promptsthe operator to confirm (or modify) the toolpath; and then executes thetoolpath as described below once confirmed by the operator.

Therefore, the robotic system can: capture a set of images, depth maps,etc. during a scan cycle; assemble this set of images into athree-dimensional model of the part; generate a toolpath based on thisthree-dimensional part model; render the three-dimensional model;project the toolpath onto the three-dimensional model; present thethree-dimensional model with projected toolpath to the operator; andprompt the operator to confirm the projected toolpath. In response toconfirmation of the toolpath by the operator, the robotic system canthen execute the toolpath during the subsequent processing cycle.

9. Processing Cycle and Toolpath Execution

In one implementation as shown in FIGS. 3-5 , the robotic systemautonomously executes the toolpath by: accessing the operator profile toretrieve a nominal translation speed; accessing the part processingprofile to retrieve the target force for the part; nominally translatingthe sanding head 120 to a translational position and a rotationalorientation, defined by the first keypoint; detecting an applied forcevalue at the sanding head 120 via a force sensor 116 configured todetect a force between the sanding pad 121 and the part surface; andselectively deviating from the toolpath at the first keypoint byadjusting the position of the sanding head 120—in a direction parallel anormal vector extending from the keypoint perpendicular to the surfaceat the keypoint—to achieve the target force on the part. The roboticsystem continues executing the toolpath by: interpolating the toolpathbetween a first keypoint and a second keypoint by interpolating a set oftranslational positions and rotational orientations between the firstkeypoint and a second keypoint; interpolating the normal vector, thetarget force, between the first keypoint and a second keypoint; andselectively deviating from the interpolated toolpath by adjusting theposition of the sanding head 120—in a direction parallel the normalvector—to achieve the target force on the part.

The controller 115 can repeat the foregoing process for each keypoint inthe set of keypoints to complete the toolpath.

9.1 Sanding Head Fixed to End Effector

In another implementation, wherein the sanding head 120 is fixed to theend effector 112, the robotic system executes a nominal toolpath by:accessing the operator profile to retrieve a nominal translation speed;translating the sanding head 120 (by translating the end effector 112),to the first keypoint defined by the first translational position androtational orientation, the sanding pad 121 centered at the firstkeypoint, and the sanding head 120 axis aligned coaxial to a vectorextending normal to the surface at the keypoint, stored in the toolpath.The robotic system continues executing the toolpath by: reading anapplied force at the sanding head 120; calculating a difference betweenthe applied force and the target force greater than a thresholddifference; and, in response, the robotic manipulator no translates thesanding head 120 along the normal vector toward or away from the firstkeypoint to reduce the difference between the applied force and thetarget force below the threshold difference, thereby achieving thetarget force at the first keypoint. The robotic system interpolates thetoolpath, translational positions and rotational orientations, thevector normal to the surface, the target force, between the firstkeypoint and a second keypoint.

The robotic system implements closed-loop controls to reduce thedifference between the applied force of the sanding head 120 against thepart surface and the interpolated target force below the thresholddifference along the interpolated path segment, and modulates theapplied force by translating the sanding head 120 along the interpolatednormal vector toward or away from the part surface, thereby deviatingfrom the toolpath, while simultaneously translating the sanding head 120along the interpolated path between the first keypoint and the secondkeypoint at the nominal translation speed.

The robotic system can repeat the foregoing for all remaining keypointsalong the toolpath.

For example, the robotic system: moves the sanding head 120 along afirst sequence of positions and orientations, defined by the first setof keypoints, relative to the first part; reads a first sequence offorce values from a force sensor 116 in the robotic system; interpolatesa first set of target force values along the first toolpath based on thetarget force values stored in the first set of keypoints; andselectively adjusts positions of the end effector 112 relative to thefirst part to maintain the first sequence of force values within athreshold difference of the first set of target force values.

In another example: the controller 115: defines the orientation of thesanding head 120 on the first part for each keypoint in the first set ofkeypoints by defining a first vector normal to a surface contour of thefirst part model at a first position on the first part defined by thefirst keypoint; and executes the toolpath, at the robotic system bynavigating the end effector 112 to the first position on the first part,and orienting the sanding head 120 to locate an axis of the sanding head120 coaxial with the first vector.

9.2 Sanding Head Mounted to Linear Actuator

In one implementation as shown in FIG. 4 , the robotic manipulator noincludes a linear actuator 118 configured to extend and retract thesanding head 120 from the end effector 112 in a direction parallel tothe axis of the sanding head 120, and including a load cell configuredto detect force values. The robotic manipulator no translates the endeffector 112 through the toolpath without deviating from the toolpathby: accessing the operator profile to retrieve the nominal translationspeed; nominally translating the sanding head 120 to a first keypointdefined by the translational position and rotational orientation,defined by the first keypoint; interpolating a set of translationalpositions and rotational orientations between the first keypoint and asecond keypoint in the toolpath; interpolating the normal vector, thetarget force, between the first keypoint and a second keypoint;detecting an applied force value at the linear actuator 118 via the loadcell; and selectively extending and retracting the linear actuator 118to achieve the target force on the part.

In one example: the robotic manipulator 110 includes: a force sensor 116coupled to the sanding head 120 and configured to output signalsrepresenting the force value of the sanding head 120 normal to localareas of the part in contact with the sanding head 120; and a linearactuator 118 configured to extend and retract the sanding head 120, onthe end effector 112, parallel to an axis of the sanding head 120.

The robotic manipulator 110 is configured to deviate from the toolpathto align the force value to the target sanding force on the part byselectively extending and retracting the linear actuator 118 based onthe force value read from the force sensor 116.

In one variation of this implementation, the linear actuator 118 is apneumatic cylinder including a pressure sensor configured to detect airpressure within the cylinder. The robotic system implements a pressuremodel to convert the detected pressure into an applied force value andcalculate a difference between the target force value and the appliedforce value. In response to a difference calculated between the appliedforce value and the target force value greater than a thresholddifference, the robotic system modulates the air pressure within thepneumatic cylinder to reduce the difference between the applied forceand the target force below the threshold difference, thereby achievingthe target force on the part.

In one example, the robotic system includes a pneumatic linear actuator118 configured to extend and retract the sanding head 120, on the endeffector 112, parallel to an axis of the sanding head 120. The roboticsystem includes: a pressure sensor coupled to the pneumatic linearactuator 118 and configured to output signals representing a pressure inthe pneumatic cylinder; and a robotic manipulator no is configured toread a sequence of pressure values at the pneumatic linear actuator 118from the pressure sensor and modulate the pressure within the pneumaticlinear actuator 118 to maintain the target force of the sanding head 120on the part.

In another variation of this implementation, the linear actuator 118 isan electromechanical linear actuator 118 configured to detect extensionand retraction resistance at the extending member of the linear actuator118. The robotic system implements a resistance model to convert thedetected resistance into an applied force value and calculate adifference between the target force value and the detected force value.

In response to a difference calculated between the applied force valueand the target force value greater than a threshold difference, therobotic system modulates the extension and retraction resistance of theelectromechanical linear actuator 118 to eliminate the differencebetween the applied force and the target force below the thresholddifference, thereby achieving the target force on the part.

In another example: The robotic system includes an electromechanicallinear actuator 118 configured to: extend and retract the sanding head120, on the end effector 112, parallel to an axis of the sanding head120; and detect extension and retraction resistance. During theprocessing period, the robotic manipulator no is configured to modulatethe extension and retraction of the electromechanical linear actuator118 based on the detected extension and retraction resistance tomaintain the target force of the sanding head 120 on the part.

9.3 Sanding Pad Wear Model

In one implementation as shown in FIG. 3 , at a first keypoint, thecontroller 115 calculates pad wear 127 and adjusts the target forcebased on pad wear 127 of the sanding pad 121 by: retrieving a length oftoolpath traversed prior to arrival at the first keypoint; accessing thesanding pad wear model to derive a pad wear 127 of the sanding pad 121at the first keypoint based on the grit 122 of the sanding pad 121; andincreasing the target force based on the pad wear 127 in Block S156.

For example, the controller 115 executes in Block S156 to access asanding pad wear model defining pad wear 127 based on the grit 122 ofthe sanding pad 121. The robotic manipulator 110 tracks the toolpathlength traversed by the sanding pad 121 attached to the sanding head 120and increases the target force value proportional to the toolpathlength, based on the sanding pad wear model.

In one variation of this example, the robotic system includes a positionsensor configured to detect the rotary speed of the sanding pad 121. Thecontroller 115 accesses a grit 122 of sanding pad 121, and the roboticsystem is configured to apply the pad wear model to: calculate a currentmaterial removal rate of the sanding pad 121 based on the pad wear 127,the grit 122 of sanding pad 121, the rotary speed of the sanding head120, the length of the toolpath traversed, and the target sanding force;and calculate a difference between the current material removal rate anda target material removal rate. In response to the difference betweenthe current material removal rate and the target material removal rateexceeding a threshold value, the robotic system modulates the appliedsanding force to reduce the difference below the threshold value toachieve the target material removal rate.

Therefore, the robotic system can autonomously translate the sandinghead 120 along a toolpath, detect the force applied to the part surfaceby the sanding head 120, and selectively deviate from the toolpath toalign the applied force to a target force defined in the part processingprofile, thereby achieving the target force across the part surface withhigh accuracy. Thus, the robotic system can implement a low-precisiontoolpath and achieve a consistent application of a target force acrosstarget zones of the surface of a part with high accuracy and highrepeatability across multiple parts.

10. Post Processing and Projection of Results

In one implementation, the controller 115 retrieves a record of thepositions and orientations of the sanding head 120 during the processingcycle and generates a process history of the processing cycle defining:processed segments of the part model, processed by the robotic systemduring the processing cycle; and unprocessed segments of the part model,not processed by the robotic system during the processing cycle.

The controller 115 annotates the three-dimensional model by projectingthe process history onto the three-dimensional model and presents theannotated three-dimensional model to the operator at the conclusion ofthe processing cycle.

By reviewing the annotated three-dimensional model, the operator canidentify areas of the part that will need to be processed again, eitherby hand, or with a different sanding head 120 or processing protocol.The operator can make a decision regarding a next action on the part byreferencing the annotated three-dimensional model.

For example, the controller 115 can present the annotatedthree-dimensional model of an automobile hood including a ram air scoop,depicting a processed zone including the area of the hood within athreshold distance of the hood edge, excluding a ram air opening of theram air scoop, and depicting an unprocessed zone including the ram airopening in the hood, and an area extending a threshold distance from theedge of the hood.

In another implementation, the robotic system (i.e., controller 115) canpresent the annotated three-dimensional model representing areas of thepart expected to be processed, but unprocessed during execution of theprocessing cycle. The operator can review the annotatedthree-dimensional model and, if necessary, make adjustments to therobotic system for future processing cycles.

In one example, the controller 115: accesses the three-dimensionalmodel; and, during a scan cycle preceding the first processing cycle,renders the three-dimensional model; projects the toolpath onto thethree-dimensional model; presents the three-dimensional model to anoperator; and prompts the operator to confirm the toolpath. Thecontroller 115 can then, following the first processing cycle: access arecord of positions of the sanding head 120 during execution of thefirst toolpath; identify a set of processed regions of the part based onthe record of positions of the sanding head 120; identify an unprocessedregion, in the set of regions, of the toolpath based on a differencebetween the toolpath and the set of processed regions; annotate thethree-dimensional model with the set of processed regions and theunprocessed region of the toolpath; and present the three-dimensionalmodel, annotated with the set of processed regions and the unprocessedregion, to the operator.

Therefore, the robotic system can output a final analysis at theconclusion of a process delineating areas of the part processed,unprocessed, expected to be processed, represented visually in athree-dimensional model of the part, and present the results to anoperator for review. The operator can thus minimize hand-finishing ofthe part by reviewing an accurate record of the areas processed.

The systems and methods described herein can be embodied and/orimplemented at least in part as a machine configured to receive acomputer-readable medium storing computer-readable instructions. Theinstructions can be executed by computer-executable componentsintegrated with the application, applet, host, server, network, website,communication service, communication interface,hardware/firmware/software elements of a user computer or mobile device,wristband, smartphone, or any suitable combination thereof. Othersystems and methods of the embodiment can be embodied and/or implementedat least in part as a machine configured to receive a computer-readablemedium storing computer-readable instructions. The instructions can beexecuted by computer-executable components integrated bycomputer-executable components integrated with apparatuses and networksof the type described above. The computer-readable medium can be storedon any suitable computer readable media such as RAMs, ROMs, flashmemory, EEPROMs, optical devices (CD or DVD), hard drives, floppydrives, or any suitable device. The computer-executable component can bea processor but any suitable dedicated hardware device can(alternatively or additionally) execute the instructions.

As a person skilled in the art will recognize from the previous detaileddescription and from the figures and claims, modifications and changescan be made to the embodiments of the invention without departing fromthe scope of this invention as defined in the following claims.

We claim:
 1. A system comprising: a robotic system: arranged adjacent toa work zone; comprising an end effector defining a sanding head and anoptical sensor, the sanding head comprising a compliant backing:configured to locate and support a sanding pad; configured toelastically deform in response to application of the sanding pad onto apart arranged within the work zone; and characterized by a compliancecoefficient; and comprising a force sensor coupled to the sanding headand configured to output signals representing a force value of thesanding head normal to local areas of the part in contact with thesanding head; configured to: during a scan period: autonomously traversean optical sensor across the part; and capture a set of optical images;during a processing period: traverse the sanding head along a toolpath;monitor the force value of the sanding head on the part via the forcesensor; and deviate from the toolpath to align the force value to atarget sanding force on the part; and a controller configured to, duringthe scan period: receive the set of optical images; assemble the set ofoptical images into a part model representing the part; access a set oftool characteristics of the sanding head mounted to the robotic system;generate the toolpath defining a sequence of positions along the partmodel; and define the target sanding force normal to local areas of thepart model based on the set of tool characteristics and proportional tothe compliance coefficient.
 2. The system of claim 1: wherein therobotic system further comprises a force sensor coupled to the sandinghead and configured to output signals representing the force value ofthe sanding head normal to local areas of the part in contact with thesanding head; and wherein the controller defines the target sandingforce normal to local areas represented in the part model and inverselyproportional to radii of local areas represented in the part model. 3.The system of claim 1: wherein the robotic system further comprises: alinear actuator configured to extend and retract the sanding head, onthe end effector, parallel to an axis of the sanding head; and whereinthe robotic system is configured to deviate from the toolpath to alignthe force value to the target sanding force on the part by selectivelyextending and retracting the linear actuator based on the force valueread from the force sensor.
 4. The system of claim 3: wherein the linearactuator comprises an electromechanical linear actuator configured to:extend and retract the sanding head, on the end effector, parallel to anaxis of the sanding head; and detect extension and retractionresistance; and wherein, during the processing period, the roboticsystem is configured to modulate the extension and retraction of theelectromechanical linear actuator based on the detected extension andretraction resistance to maintain the target force of the sanding headon the part.
 5. The system of claim 3: wherein the linear actuatorcomprises a pneumatic linear actuator configured to extend and retractthe sanding head, on the end effector, parallel to an axis of thesanding head; further comprising a pressure sensor coupled to thepneumatic linear actuator and configured to output signals representinga pressure in a pneumatic cylinder; and wherein the robotic system isconfigured to: read a sequence of pressure values at the pneumaticlinear actuator from the pressure sensor; and modulate the pressurewithin the pneumatic linear actuator to maintain the target force of thesanding head on the part.
 6. The system of claim 1: wherein the roboticsystem comprises a torque sensor coupled to the sanding head andconfigured to output signals representing torque values between thesanding pad on the sanding head and local areas of the part in contactwith the sanding pad; wherein the controller defines target sandingtorques across the part proportional to radii of local surface contoursrepresented in the part model; and wherein the robotic system isconfigured to modulate a sanding pad speed of the sanding head to aligntorque values, between the sanding pad and local areas of the part, tothe target sanding torques while traversing the sanding head along thetoolpath.
 7. The system of claim 1, wherein the robotic systemcomprises: a multi-link robotic arm configured to manipulate the endeffector through six degrees of freedom proximal the part positioned inthe work zone; and a linear conveyor configured to translate themulti-link robotic arm a length of the work zone.
 8. A methodcomprising: accessing a part model representing surface contours of apart loaded into a work zone proximal a robotic system; accessing a setof tool characteristics of a sanding head manipulated by the roboticsystem, the set of tool characteristics comprising a geometry and abacking compliance of the sanding head; retrieving a toolpath pattern;retrieving a set of nominal processing parameters; projecting thetoolpath pattern onto the part model to define a toolpath; defining aset of regions along the toolpath; for each region, in the set ofregions, of the toolpath: detecting a local curvature radius of thesurface contours represented in the part model proximal the region ofthe toolpath; calculating a contact area between the sanding head andthe part proximal the region based on the geometry, the backingcompliance, and the local curvature radius; and defining a target forcevalue, in a set of target force values, of the sanding head normal tolocal areas on the part based on the backing compliance, the contactarea, and the set of nominal processing parameters; and during aprocessing cycle, at the robotic system: traversing the sanding headalong the toolpath; reading a sequence of force values from a forcesensor arranged in the robotic system, the force sensor configured tooutput signals representing force of the sanding head on and normal tolocal areas of the part in contact with the sanding head; and deviatingfrom the toolpath to maintain the sequence of force values within athreshold difference of the set of target force values.
 9. The method ofclaim 8: wherein retrieving the set of nominal processing parameterscomprises retrieving a nominal translation speed of the sanding head;wherein defining the target force value for each region of the toolpathcomprises, for each region of the toolpath, defining the target forcevalue of the sanding head on the part: proportional to a contact areabetween the sanding head and the part proximal the region; proportionalto the backing compliance of the sanding head; and proportional to thenominal translation speed; and wherein reading the sequence of forcevalue values from the force sensor in the robotic system comprisesreading the sequence of force values from the force sensor coupled tothe sanding head.
 10. The method of claim 9: further comprisingaccessing a maximum applied pressure for the part; and wherein definingthe target force value of the sanding head on the part for each regionof the toolpath comprises, for each region of the toolpath: calculatinga maximum force for the region based on the maximum applied pressure anda contact area between the sanding head and the part proximal theregion; and defining the target force value of the sanding head on thepart less than the maximum force.
 11. The method of claim 10, whereincalculating the contact area for each region of the toolpath comprises,for each region of the toolpath: calculating an intersection of thegeometry of the sanding head, projected onto the region in the partmodel, and the part model; and calculating the contact area for theregion based on the intersection.
 12. The method of claim 8: whereinaccessing the set of tool characteristics of the sanding head comprisesaccessing the set of tool characteristics comprising a gritspecification of the sanding pad; wherein retrieving the set of nominalprocessing parameters comprises retrieving a minimum material removaldepth for the part and a maximum toolpath execution duration; whereindefining the target force value for each region of the toolpathcomprises, for each region of the toolpath: assigning a targettranslation speed to the region inversely proportional to the maximumtoolpath execution duration; and assigning the target force value to theregion: proportional to a contact area of the sanding head on the partproximal the region; inversely proportional to the grit specification ofthe sanding pad; proportional to the backing compliance of the sandinghead; proportional to the minimum material removal depth; andproportional to the target translation speed; wherein traversing thesanding head along the toolpath comprises traversing the sanding headalong the toolpath according to target sanding head translational speedsassigned to regions of the toolpath; and wherein reading the sequence offorce values from the force sensor in the robotic system comprisesreading the sequence of force values from the force sensor coupled tothe sanding head.
 13. The method of claim 8: further comprisingaccessing a sanding pad wear model defining sanding pad wear based on asanding grit of a sanding pad; and wherein defining the target forcevalue for each region of the toolpath comprises, for each region of thetoolpath: tracking the toolpath traversed by the sanding pad attached tothe sanding head; and assigning the target force value furtherproportional to a length of the toolpath traversed and based on thesanding pad wear model.
 14. The method of claim 13: further comprising:accessing the sanding grit; and detecting the rotational speed of thesanding pad; and wherein defining the target force value for each regionof the toolpath comprises, for each region of the toolpath: calculatinga current material removal rate of the sanding pad based on the sandingpad wear model, the sanding grit, the rotational speed of the sandinghead, and the length of the toolpath traversed; calculating a differencebetween the current material removal rate and target material removalrate; and in response to a difference between the current materialremoval rate and the target material removal rate exceeding a thresholdvalue, assigning the target force value to reduce the difference belowthe threshold value to achieve the target material removal rate.
 15. Themethod of claim 8: wherein defining the target force value for eachregion of the toolpath comprises: for a region of the toolpath within afirst zone, assigning a first target force value based on a firstcoating thickness; and for a second region of the first toolpath withina second zone, assigning a second target force value, less than thefirst force value, based on a second coating thickness; wherein readingthe sequence of force values from the force sensor in the robotic systemcomprises reading the sequence of force values from the force sensorcoupled to the sanding head; and wherein deviating from the toolpathcomprises deviating from the toolpath to maintain the sequence of forcevalues within the threshold difference of the set of target forcevalues.
 16. The method of claim 15, further comprising defining aprocessing order for the set of regions of the toolpath, the firstregion preceding the second region in the processing order based on thefirst coating thickness exceeding the second coating thickness.
 17. Themethod of claim 8: wherein accessing the part model comprises accessingthe part model comprising a color three-dimensional model; furthercomprising, during a scan cycle preceding the processing cycle:rendering the color three-dimensional model; projecting the toolpathonto the color three-dimensional model; presenting the colorthree-dimensional model to an operator; and prompting the operator toconfirm the toolpath; and further comprising, following the processingcycle: accessing a record of positions of the sanding head duringexecution of the toolpath; identifying a set of processed regions of thepart based on the record of positions of the sanding head; identifyingan unprocessed region, in the set of regions, of the toolpath based on adifference between the toolpath and the set of processed regions;annotating the color three-dimensional model with the set of processedregions and the unprocessed region of the toolpath; and presenting thecolor three-dimensional model, annotated with the set of processedregions and the unprocessed region, to the operator.
 18. A methodcomprising: accessing apart model representing surface contours of apartloaded into a work zone adjacent a robotic system; accessing a geometryof a sanding head manipulated by the robotic system, the sanding headcomprising a compliant backing: configured to locate and support asanding pad; configured to elastically deform in response to applicationof the sanding pad onto a part arranged within the work zone; andcharacterized by a backing compliance; retrieving a toolpath pattern;projecting the toolpath pattern onto the part model to define atoolpath; defining a set of regions along the toolpath; for each region,in the set of regions, of the toolpath: detecting a local curvatureradius of surface contours represented in the part model proximal theregion of the toolpath; calculating a contact area between the sandinghead and the part proximal the region and the local curvature radius;and defining a target force value, in a sequence of target force values,of the sanding head on and normal to the region of the part based on thecontact area and proportional to the backing compliance; and during aprocessing cycle, at the robotic system: traversing the sanding headalong the toolpath; reading a sequence of force values from a forcesensor coupled to the sanding head, the force sensor configured tooutput signals representing force of the sanding head on and normal tolocal areas of the part in contact with the sanding head; and deviatingfrom the toolpath to maintain the sequence of force values within athreshold difference of the sequence of target force values.